1. Field of the Invention
This invention relates to magnetic recording media which have improved magnetic characteristics, and excellent abrasion resistance and travelling stability.
2. Description of the Prior Art
Magnetic recording media such as magnetic tapes should have not only good electromagnetic conversion characteristics, but also good travelling stability and good retentivity of their shape when reeled. Especially, when magnetic tapes are used in video tape recorders, they should have a low transmittance against light having a wavelength of 8000-9000 angstrom because most existing video tape recorders have a photosensor as a tape end detector.
As is well known in the art, the magnetic layer of a magnetic tape is usually composed of a magnetic powder and a binder. In order to improve characteristic properties of the magnetic layer such as an abrasion resistance, travelling stability, light transmittance and the like, various additives are added to the mixture of a magnetic powder and a binder. For instance, surface active agents or carbon black which serves as an antistatic agent are used in order to reduce the surface electric conductivity of the magnetic layer. Magnetic recording media whose magnetic layer comprises surface active agents are not favorable because their surface conductivity depends largely on an ambient humidity. In addition, surface active agents are not effective in improving the light-shielding property. On the other hand, with magnetic recording media having carbon black contained in a magnetic layer thereof, low molecular weight additives are subject to absorption by carbon black if the carbon black is used in large amounts so as to lower light transmittance. This leads to disadvantages such as lowering of electromagnetic characteristics, and deterioration of an abrasion resistance and a travelling performance of the media. The carbon black does not show its effect unless used in relatively large amounts, so that excellent electromagnetic characteristics, abrasion resistance and travelling property cannot be expected when using carbon black and surface active agent in combination.